System for detecting abnormality of yaw rate sensor and lateral acceleration sensor

ABSTRACT

Abnormality of a yaw rate sensor, including a state in which the neutral point is normal, but the sensitivity is abnormal, is detected with high accuracy, irrespective of the situation of a road surface traveled. A lower one of an output from a dividing device for dividing a vehicle speed detected by the vehicle speed detecting device by a minimum radius of turning of a vehicle and an output from a dividing device for dividing a gravitational acceleration by the vehicle speed detected by the vehicle speed detecting device, is selected in a low-select device. It is determined in an abnormality determining device that the yaw rate sensor is abnormal when a yaw rate detected by the yaw rate sensor exceeds a value selected in the low-select device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system for detecting an abnormalityof a yaw rate sensor for detecting a yaw rate of a vehicle, and a systemfor detecting an abnormality of a lateral acceleration sensor fordetecting a lateral acceleration of the vehicle.

2. Description of the Related Art

To detect the abnormality of the yaw rate sensor, it is a conventionalpractice to determine that the yaw rate is abnormal when the valuedetected by the yaw rate sensor exceeds an upper limit value or a lowerlimit value, and to determine the abnormality of the yaw rate sensor bycomparison of the yaw rate presumed from a difference between left andright wheel speeds with the value detected by the yaw rate sensor.

In the technique for determining whether the yaw rate sensor is abnormalbased on whether the value detected by the yaw rate sensor exceeds theupper or lower limit value, it is impossible to detect a state in whichthe neutral point of the yaw rate sensor is normal, but the sensitivityis abnormal. In the technique for determining whether the yaw ratesensor is abnormal by the comparison of the yaw rate presumed from adifference between the left and right wheel speeds with the valuedetected by the yaw rate sensor, the yaw rate presumed from thedifference between the left and right wheel speeds is inaccurate whenthe vehicle is traveling on a rough road or on a road surface having alow friction coefficient, on which the wheel is liable to slip. For thisreason, it is impossible to determine the abnormality of the yaw ratesensor with good accuracy.

SUMMARY OF THE INVENTION

The present invention has been accomplished with such circumstance inview, and it is a first object of the present invention to provide asystem for detecting an abnormality of a yaw rate, wherein theabnormality of a yaw rate sensor, including a state in which the neutralpoint of the yaw rate sensor is normal, but the sensitivity is abnormal,can be detected with good accuracy, irrespective of the situation of aroad surface traveled. It is a second object of the present invention toprovide a system for detecting an abnormality of a lateral accelerationsensor, wherein the abnormality of the lateral acceleration sensor canbe detected with good accuracy, based on the measure enabling theabnormality of the yaw rate sensor to be detected with good accuracy.

To achieve the first object, there is provided a system for detecting anabnormality of a yaw rate sensor, comprising a vehicle speed detectingmeans for detecting a vehicle speed of a vehicle, a dividing means fordividing the vehicle speed detected by the vehicle speed detecting meansby a minimum turning radius of the vehicle, a dividing means fordividing a gravitational acceleration by the vehicle speed detected bythe vehicle speed detecting means, a low-select means for selecting alower one of outputs from both of the dividing means, and an abnormalitydetermining means for determining that a yaw rate sensor is abnormalwhen the yaw rate detected by the yaw rate sensor exceeds a valueselected by the low-select means.

When there is no side-slip of the vehicle, the yaw rate γ of the vehiclemust be within an obliquely-lined range shown in FIG. 3 depending upon alimit value of centripetal acceleration of the vehicle, i.e., thegravitational acceleration G and a lower limit value of the radius ofturning of the vehicle, i.e., the minimum turning radius R. If thevehicle speed is represented by V, the yaw rate γ of the vehicle capableof being generated must be in a range of γ≦min{(V/R), (G/V)}. Therefore,when the yaw rate γ is in a range which exceeds lower one of a value(V/R) obtained by dividing the vehicle speed V by the minimum radius Rof turning of the vehicle and a value (G/V) obtained by dividing thegravitational acceleration G by the vehicle speed V, i.e., which exceedsmin{(V/R), (G/V)}, the side-slip of the vehicle is nearly "0" in a usualtraveling state of the vehicle. Therefore, the abnormality of the yawrate sensor, including the state in which the neutral point is normal,but the sensitivity is abnormal, can be detected with good accuracy,irrespective of the situation of the road surface traveled.

To achieve the first object, there is also provided a system fordetecting an abnormality of a yaw rate sensor, comprising a vehiclespeed detecting means for detecting a vehicle speed of a vehicle, asteering angle sensor for detecting a steering angle of a steeringwheel, a multiplying means for multiplying the steering angle detectedby the steering angle sensor by the vehicle speed detected by thevehicle speed detecting means and by a given constant, a dividing meansfor dividing a gravitational acceleration by the vehicle speed detectedby the vehicle speed detecting means, a low-select means for selecting alower one of outputs from the multiplying means and the dividing means,and an abnormality determining means for determining that a yaw ratesensor is abnormal when a yaw rate detected by the yaw rate sensorexceeds a value selected by the low-select means.

When the steering angle detected by the steering angle sensor isrepresented by δ, and a constant is represented by k, the radius ofturning of the vehicle is capable of being presumed with {1/(δ·k)},until the centripetal acceleration becomes a limit value. If (V/R) inFIG. 3 is replaced by (δ·V·k), the range of yaw rate γ capable of beingactually produced can be determined more precisely than anobliquely-lined range shown in FIG. 3. Therefore, when the yaw rate γ isin a range which exceeds a lower one of a value (δ·V·k) obtained bymultiplying the steering angle δ by the vehicle speed V and the givenconstant k and a value (G/V) obtained by dividing the gravitationalacceleration G by the vehicle speed, i.e., which exceeds min{(δ·V·k),(G/V)}, the side-slip of the vehicle is nearly "0" in a normal travelingstate. Therefore, the abnormality of the yaw rate sensor, including thestate in which the neutral point is normal, but the sensitivity isabnormal, can be detected with a good accuracy, irrespective of thesituation of a road surface traveled.

To achieve the first object, there is also provided a system fordetecting an abnormality of a yaw rate sensor, comprising a vehiclespeed detecting means for detecting a vehicle speed of a vehicle, alateral acceleration sensor for detecting a lateral acceleration of thevehicle, a dividing means for dividing the vehicle speed detected by thevehicle speed detecting means by a minimum turning radius of thevehicle, a dividing means for dividing the lateral acceleration detectedby the lateral acceleration sensor by the vehicle speed detected by thevehicle speed detecting means, a low-select means for selecting a lowerone of outputs from both of the dividing means, and an abnormalitydetermining means for determining that a yaw rate sensor is abnormalwhen a yaw rate detected by the yaw rate sensor exceeds the valueselected by the low-select means.

When the lateral acceleration detected by the lateral accelerationsensor is represented by α, the range of yaw rate capable of beingactually produced can be determined more precisely than the obliquelylined range shown in FIG. 3 by replacing (G/V) in FIG. 3 by (α/V).Therefore, when the yaw rate γ is in a range which exceeds lower one ofa value (V/R) obtained by dividing the vehicle speed V by the minimumradius of turning of the vehicle and a value (α/V) obtained by dividingthe lateral acceleration α by the vehicle speed V, i.e., which exceedsmin{(V/R), (α/V)}, the side-slip of the vehicle is nearly "0" in a usualtraveling state. Thus, the abnormality of the yaw rate sensor, includingthe state in which the neutral point is normal, but the sensitivity isabnormal, can be detected with a good accuracy, irrespective of thesituation of a road surface traveled.

To achieve the first object, there is also provided a system fordetecting an abnormality of a yaw rate sensor, comprising a vehiclespeed detecting means for detecting a vehicle speed of a vehicle, asteering angle sensor for detecting a steering angle of a steeringwheel, a lateral acceleration sensor for detecting a lateralacceleration of the vehicle, a multiplying means for multiplying thesteering angle detected by the steering angle sensor by the vehiclespeed detected by the vehicle speed detecting means and by a givenconstant, a dividing means for dividing the lateral accelerationdetected by the lateral acceleration sensor by the vehicle speeddetected by the vehicle speed detecting means, a low-select means forselecting a lower one of outputs from the multiplying means and thedividing means, and an abnormality determining means for determiningthat a yaw rate sensor is abnormal when a yaw rate detected by the yawrate sensor exceeds the value selected by the low-select means.

When the steering angle detected by the steering angle sensor isrepresented by δ, and a constant is represented by k, the radius ofturning of the vehicle is capable of being presumed with {1/(δ·k)},until the centripetal acceleration becomes a limit value. By replacing(V/R) in FIG. 3 by (δ·V·k), the range of yaw rate γ capable of beingactually produced can be determined more precisely than theobliquely-lined range shown in FIG. 3. When the lateral accelerationdetected by the lateral acceleration sensor is represented by α, therange of yaw rate capable of actually being produced can be determinedmore precisely than the obliquely-lined range shown in FIG. 3 byreplacing (G/R) in FIG. 3 by (α/V). Therefore, when the yaw rate γ is ina range which exceeds a lower one of a value (δ·V·k) obtained bymultiplying the steering angle δ by the vehicle speed V and the givenconstant k and a value (α/V) obtained by dividing the lateralacceleration α by the vehicle speed V, i.e., which exceeds min{(δ·V·k),(α/V)}, the side slip of the vehicle is nearly "0" in a normal travelingstate. Thus, the abnormality of the yaw rate sensor, including the statein which the neutral point is normal, but the sensitivity is abnormal,can be detected with a good accuracy, irrespective of the situation of aroad surface traveled.

To achieve the second object, there is provided a system for detectingan abnormality of a lateral acceleration sensor, comprising a vehiclespeed detecting means for detecting a vehicle speed of a vehicle, adividing means for dividing a squared value of the vehicle speeddetected by the vehicle speed detecting means by a minimum turningradius of the vehicle, a low-select means for selecting lower one of anoutput from the dividing means and a gravitational acceleration, and anabnormality determining means for determining that the lateralacceleration sensor is abnormal when the lateral acceleration detectedby the lateral acceleration sensor exceeds a value selected by thelow-select means.

When the yaw rate is represented by γ; the lateral acceleration isrepresented by α, and the vehicle speed is by V, a relation γ=(α/V) isestablished in a range of smaller side slip. If the obliquely-linedrange of yaw rate γ show n in FIG. 3, i.e., min{(V/R), (G/V)} isreplaced by the lateral acceleration α, a relation, α≦min{(V² /R), G} isgiven. Therefore, the lateral acceleration α capable of being actuallyproduced must be in a range of α≦min{(V² /R), G}. When the lateralacceleration α is in a range which exceeds lower one of a value (V² /R)obtained by dividing a squared value of the vehicle speed V and agravitational acceleration G, i.e., which exceeds min{(V² /R), G}, theside slip of the vehicle is nearly "0" in a normal traveling state.Thus, the abnormality of the yaw rate sensor, including the state inwhich the neutral point is normal, but the sensitivity is abnormal, canbe detected with good accuracy, irrespective of the situation of a roadsurface traveled.

To achieve the second object, there is also provided a system fordetecting an abnormality of a lateral acceleration sensor, comprising avehicle speed detecting means for detecting a vehicle speed of avehicle, a steering angle sensor for detecting a steering angle of asteering wheel, a multiplying means for multiplying the steering angledetected by the steering angle sensor by a squared value of the vehiclespeed detected by the vehicle speed detecting means and by a givenconstant, a low-select means for selecting lower one of an output fromthe multiplying means and a gravitational acceleration, and anabnormality determining means for determining that the lateralacceleration sensor is abnormal when a lateral acceleration detected bythe lateral acceleration sensor exceeds a value selected by thelow-select means.

When the steering angle detected by the steering angle sensor isrepresented by δ, and a constant is by k, the turning radius of thevehicle is capable of being presumed with {1/(δ·k)}, until thecentripetal acceleration becomes a limit value. By ensuring that therange of yaw rate capable of being actually produced is in a range ofγ≦min{(δ·V·k), (G/V)} by replacing (V/R) in FIG. 3 by (δ·V·k), the rangeof yaw rate capable of being actually produced can be determined moreprecisely than the obliquely-lined range shown in FIG. 3. Moreover, whenthe yaw rate is represented by γ; the lateral acceleration isrepresented by α, and the vehicle speed is represented by V, a relation,γ=(α/V) is established in a range of smaller side-slip. If the rane ofyaw rate γ determined by γ≦min{(δ·V·k), (G/V)} is replaced by thelateral acceleration α, a relation, α≦min{(δ·V·k), (G/V)} is given.Therefore, when the lateral acceleration α is in a range which exceeds alower one of a value obtained by multiplying the steering angle δ by asquared value (V²) of the vehicle and the given constant k and agravitational acceleration G, i.e., which exceeds min{(δ·V² ·k), G}, theside-slip of the vehicle is nearly "0" in a normal traveling state ofthe vehicle. Thus, the abnormality of the yaw rate sensor, including thestate in which the neutral point is normal, but the sensitivity isabnormal, can be detected with high accuracy, irrespective of thesituation of a road surface traveled.

In addition, the abnormality determining means determines that thelateral acceleration sensor is abnormal when a lateral accelerationdetected by the lateral acceleration sensor exceeds the output from thelow-select means, both of when the vehicle is being turned leftwards andrightwards.

An offset value component corresponding to the sloping of a road surfaceis included in the value detected by the lateral acceleration sensor. Ifthe output from the low-select means is compared only with the valuedetected by the lateral acceleration sensor there is a possibility thatthe erroneous-determination may be made due to the value detected by thelateral acceleration sensor and including the offset value component.However, it is determined that the lateral acceleration sensor isabnormal when the abnormality determining means determines theabnormality, both of when the vehicle is being turned leftwards andrightwards. Therefore, the erroneous-determination due to the sloping ofthe road surface can be avoided, whereby the abnormality of the lateralacceleration sensor can be determined with good accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a driving system and a brake system of avehicle according to a first embodiment of the present invention.

FIG. 2 is a block diagram of an arrangement for determiningabnormalities of a yaw rate sensor and a lateral acceleration sensor,which is extracted from a control unit.

FIG. 3 is a diagram showing a range of yaw rate which is capable ofactually being generated.

FIG. 4 is a block diagram similar to FIG. 2, but according to a secondembodiment of the present invention.

FIG. 5 is a block diagram similar to FIG. 2, but according to a thirdembodiment of the present invention.

FIG. 6 is a block diagram similar to FIG. 2, but according to a fourthembodiment of the present invention.

FIG. 7 is a block diagram similar to FIG. 2, but according to a fifthembodiment of the present invention.

FIG. 8 is a flow chart showing a procedure for determining anabnormality of a lateral acceleration sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described by way of embodiments shownin the accompanying drawings.

FIGS. 1 to 3 show a first embodiment of the present invention. FIG. 1 isa diagram showing a driving system and a brake system of a vehicle; FIG.2 is a block diagram of an arrangement for determining an abnormality ofa yaw rate sensor and a lateral acceleration sensor, which is extractedfrom a control unit; and FIG. 3 is a diagram showing a range of yaw ratewhich is capable of being actually generated.

Referring first to FIG. 1, the vehicle is a front engine, front drivevehicle. A power unit P comprising an engine E and a transmission T ismounted at a front portion of a vehicle body 1 to drive a left frontwheel W_(FL) and a right front wheel W_(FR) which are driving wheels.Left and right front wheel brakes B_(FL) and B_(FR) are mounted on theleft and right front wheels W_(FL) and W_(FR), respectively, and leftand right rear wheel brakes B_(RL) and B_(RR) are mounted on left andright rear wheels W_(RL) and W_(RR) which are follower wheels,respectively. Each of the wheel brakes B_(FL), B_(FR), B_(RL) and B_(RR)is, for example, a disc brake.

A braking liquid pressure corresponding to an operation of depression ofa brake pedal 3 is outputted from first and second output ports 2A and2B provided in a tandem-type master cylinder M. The first and secondoutput ports 2A and 2B are connected to a braking liquid pressurecontrol device 4 as a vehicle motion regulating means, so that thebraking liquid pressure from the braking liquid pressure control device4 is applied to the wheel brakes B_(FL), B_(FR), B_(RL) and B_(RR). Inthe braking liquid pressure control device 4, the braking fluid pressureapplied to the wheel brakes B_(FL), B_(FR), B_(RL) and B_(RR) iscontrolled by a control unit 5. Inputted to the control unit 5 aredetection values which are detected by wheel speed sensors 6_(FL),6_(FR), 6_(RL) and 6_(RR) for detecting wheel speeds of the wheelsW_(FL), W_(FR), W_(RL) and W_(RR), respectively, a steering angle sensor7 for detecting a steering angle δs resulting from the operation of asteering wheel H, a yaw rate sensor 8 for detecting a yaw rate γ of thevehicle, and a lateral acceleration sensor 9 for detecting a lateralacceleration α of the vehicle.

The control unit 5 is capable of carrying out (1) an antilock brakecontrol for controlling the braking liquid pressures for the wheelbrakes B_(FL), B_(FR), B_(RL) and B_(RR) to eliminate the locking of thewheels during a braking operation; (2) a traction control forcontrolling the braking liquid pressures for the left and right frontwheel brakes B_(FL) and B_(FR), which are mounted on the left and rightfront wheels W_(FL) and W_(FR), which are driving wheels, therebyinhibiting the generation of excessive slipping of the left and rightfront wheels W_(FL) and W_(FR) during non-braking operation; and (3) adirectional stability control for controlling the braking liquidpressures for the left and right front wheel brakes B_(FL) and B_(FR)irrespective of whether during the braking and non-braking operations tocontrol the yaw motion of the vehicle. For example, in the control unit5, for each of the antilock brake control, the traction control and thedirectional stability control, a reference speed is determined for atleast one of the driving wheels W_(FL) and W_(FR) and the followerwheels W_(RL) and W_(RR) ; and a control quantity is calculated based ona deviation between the actual wheel speed of at least one of thedriving wheels W_(FL) and W_(FR) and the follower wheels W_(RL) andW_(RR) and the reference speed, and the operation of the braking liquidpressure control device 4 is controlled based on the control quantity.In this case, the reference value is corrected based on at least one ofthe yaw rate γ and the lateral acceleration α. For example, in thetraction control, the reference value is corrected to be decreased whenat least one of the yaw rate γ and the lateral acceleration α is larger.

The braking liquid pressure control device 4 and a means for regulatingthe output from the engine E may be used as a motion regulating meansfor varying the motion of the vehicle, or a means for regulating theoutput from the engine E may be used in place of the braking liquidpressure control device 4.

The control unit 5 also has a function for detecting an abnormality ofthe yaw rate sensor 8 and the lateral acceleration sensor 9. To detectthe abnormality of the yaw rate sensor 8 and the lateral accelerationsensor 9, as shown in FIG. 2, the control unit 5 includes a vehiclespeed presuming means 11 as a vehicle speed detecting means, a firstdividing means 12, a second dividing means 13, a low-select means 14 forselecting lower one of outputs from the first and second dividing means12 and 13, a yaw rate sensor abnormality determining means 15 fordetermining the abnormality of the yaw rate sensor 8 based on the outputfrom the low-select means 14 and the yaw rate γ detected by the yaw ratesensor 8, a third dividing means 16, a low-select means 17 for selectinga lower one of an output from the third dividing means 16 and agravitational acceleration G, and a lateral acceleration sensorabnormality determining means 18 for determining the abnormality of thelateral acceleration sensor 9 based on an output from the low-selectmeans 17 and the lateral acceleration α detected by the lateralacceleration sensor 9.

The vehicle speed presuming means, 11 presumes a vehicle speed V basedon the wheel speeds of at least the left and right follower wheels,i.e., the left and right rear wheels W_(RL) and W_(RR). In thisembodiment, a vehicle speed V based on the wheel speeds detected by thewheel speed sensors 6_(FL), 6_(FR), 6_(RL) and 6_(RR) is calculated inthe vehicle speed presuming means 11, and the vehicle speed V obtainedin the vehicle speed presuming means 11 is inputted to the first, secondand third dividing means 12, 13 and 16.

The first dividing means 12 carries out the calculation of dividing thevehicle speed V by the minimum turning radius R of the vehicle, and thesecond dividing means 13 carries out the calculation of dividing thegravitational acceleration G by the vehicle speed V. A value (V/R)obtained in the first dividing means 12 and a value (G/V) obtained inthe second dividing means 13 are inputted to the low-select means 14,and a lower one of the values (V/R) and (G/V) is selected by thelow-select means 14 and inputted to the yaw rate sensor abnormalitydetermining means 15. A yaw rate γ detected by the yaw rate sensor 8 isalso inputted to the yaw rate sensor abnormality determining means 15.

In the yaw rate sensor abnormality determining means 15, the valueselected by the low-select means 14, i.e., min {(V/R), (G/V)} and theyaw rate γ are compared with one another. If γ>min {(V/R), (G/V)}, thenthe yaw rate sensor abnormality determining means 15 determines that theyaw rate sensor 8 is abnormal, thereby outputting a signal indicative ofthe fact that the yaw rate sensor 8 is abnormal.

The third dividing means 16 carries out the calculation of dividing asquared value (V²) of the vehicle speed V by the minimum turning radiusR of the vehicle. A value (V² /R) obtained in the third dividing means16 and the gravitational acceleration G are inputted to the low-selectmeans 17. The low-select means 17 selects a lower one of the value (V₂/R) obtained in the third dividing means 16 and the gravitationalacceleration G, and the value obtained in the low-select means 17, i.e.,min{(V² /R), G} is inputted to the lateral acceleration sensorabnormality determining means 18. A lateral acceleration α detected bythe lateral acceleration sensor 9 is also inputted to the lateralacceleration sensor abnormality determining means 18. In the lateralacceleration sensor abnormality determining means 18, the valuemin{(V²), G} obtained in the low-select means 17 and the lateralacceleration α detected by the lateral acceleration sensor 9 arecompared with each other. If α>min{(V²), G}, then the lateralacceleration sensor abnormality determining means 18 determines that thelateral acceleration sensor 9 is abnormal, thereby outputting a signalindicative of the fact that the lateral acceleration sensor 9 isabnormal.

The operation of the first embodiment will be described below. Whenthere is no side-slipping of the vehicle, the yaw rate γ of the vehiclemust be within an obliquely-lined range shown in FIG. 3, depending upona limit value of centripetal acceleration of the vehicle, i.e., thegravitational acceleration G of the vehicle and a lower limit value ofthe radius of turning of the vehicle, i.e., the minimum turning radiusR, and thus, a relation, γ≦min{(V/R), (G/V)} must be established. Ifγ>min{(V/R), (G/V)}, the yaw rate sensor 8 outputs a value which cannotbe intrinsically produced. Moreover, the side-slip of the vehicle isnearly "zero" in a normal traveling state and hence, the abnormality ofthe yaw rate sensor 8 including a state in which a neutral point isnormal, but the sensitivity is abnormal, can be detected with a goodaccuracy, irrespective of the situation of a road surface traveled.

In a range of a small side-slip, γ=(α/V) is established. When theobliquely-lined range shown in FIG. 3, i.e., γ≦min{(V/R), (G/V)}, isreplaced by the lateral acceleration α, a relation, α≦min{(V² /R), G} isgiven. Therefore, the lateral acceleration α capable of being generatedin the vehicle must be in a range of α≦min{(V² /R), G}. When α>min{(V²/R), G}, the lateral acceleration sensor 9 outputs a value which cannotbe intrinsically produced. Thus, the abnormality of the lateralacceleration sensor 9 including a state in which a neutral point isnormal, but the sensitivity is abnormal, can be detected with goodaccuracy, irrespective of the situation of a road surface traveled.

FIG. 4 shows a second embodiment of the present invention, whereinportions or components corresponding to those in the first embodimentare designated by like reference characters.

To detect the abnormality of the yaw rate sensor 8 and the lateralacceleration sensor 9, the control unit 5 includes a vehicle speedpresuming means 11, a multiplying means 19, a dividing means 13, alow-select means 20 for selecting a lower one of outputs from themultiplying means 19 and the dividing means 13, a yaw rate sensorabnormality determining means 21 for determining the abnormality of theyaw rate sensor 8 based on an output from the low-select means 20 and ayaw rate detected by the yaw rate sensor 8, a dividing means 16, alow-select means 17 for selecting a lower one of an output from thedividing means 16 and the gravitational acceleration G, and a lateralacceleration sensor abnormality determining means 18 for determining theabnormality of the lateral acceleration sensor 9 based on an output fromthe low-select means 17 and the lateral acceleration α detected by thelateral acceleration sensor 9.

The steering angle δ detected by the steering angle sensor 7 and thevehicle speed V obtained in the vehicle speed presuming means 11 areinputted to the multiplying means 19. The multiplying means 19 carriesout the calculation of multiplying the steering angle δ by the vehiclespeed V and a given constant k, and the low-select means 20 selects alower one of a value (δ·V·k) obtained in the multiplying means 19 and avalue (G/V) obtained in the dividing means 13, and inputs such lower oneto the yaw rate sensor abnormality determining means 21. In the yaw ratesensor abnormality determining means 21, the value outputted from thelow-select means 20, i.e., min{(δ·V·k), (G/V)} and the yaw rate γdetected by the yaw rate sensor 8 are compared with each other. Ifγ>min{(δ·V·k), (G/V)}, then the yaw rate sensor abnormality determiningmeans 21 determines that the yaw rate sensor 8 is abnormal, therebyoutputting a signal indicative of the fact that the yaw rate sensor 8 isabnormal.

The turning radius of the vehicle is capable of being presumed with{1/(γk)}, until the centripetal acceleration becomes a limit value. Arange of yaw rate γ capable of being actually produced can be determinedmore precisely than the obliquely-lined range shown in FIG. 3 byreplacing (V/R) in FIG. 3 by (δ·V·k). Therefore, in the secondembodiment in which, when γ>min{(δ·V·k), (G/V)}, it is determined thatthe yaw rate sensor 8 is abnormal, the abnormality of the yaw ratesensor 8 can be detected with greater accuracy.

FIG. 5 shows a third embodiment of the present invention, where portionsor components corresponding to those in each of the above-describedembodiments are designated by like reference characters.

To detect the abnormality of the yaw rate sensor 8 and the lateralacceleration sensor 9, the control unit 5 includes a vehicle speedpresuming means 11, dividing means 12 and 22, a low-select means 23 forselecting lower one of outputs from both the dividing means 12 and 22, ayaw rate sensor abnormality determining means 24 for determining theabnormality of the yaw rate sensor 8 based on an output from thelow-select means 23 and a yaw rate δ detected by the yaw rate sensor 8,a dividing means 16, a low-select means 17 for selecting lower one of anoutput from the dividing means 16 and the gravitational acceleration G,and a lateral acceleration sensor abnormality determining means 18 fordetermining the abnormality of the lateral acceleration sensor 9 basedon an output from the low-select means 17 and the lateral acceleration αdetected by the lateral acceleration sensor 9.

The vehicle speed V obtained in the vehicle speed presuming means 12 andthe lateral acceleration α detected by the lateral acceleration sensor 9are inputted to the dividing means 22. The dividing means 22 carries outthe calculation of dividing the lateral acceleration α by the vehiclespeed V. The low-select means 23 selects a lower one of a value (V/R)obtained in one of the dividing means 12 and a value (α/V) obtained inthe other dividing means 22, and inputs such lower one to the yaw ratesensor abnormality determining means 24. In the yaw rate sensorabnormality determining means 24, a value outputted from the low-selectmeans 23, i.e., min{(V/R), (α/V)} and the yaw rate γ detected by the yawrate sensor 8 are compared with each other. If γ>min{(V/R), (α/V)}, theyaw rate sensor abnormality determining means 24 determines that the yawrate sensor 8 is abnormal, thereby outputting a signal indicative of thefact that the yaw rate sensor 8 is abnormal.

In the obliquely-lined range shown in FIG. 3, (G/R) is based on thelimit value of the lateral acceleration α and hence, a range of yaw rateγ capable of being actually produced can be determined more preciselythan the obliquely-lined range shown in FIG. 3. Therefore, in the thirdembodiment in which when γ>min{(V/R), (α/V)}, it is determined that theyaw rate sensor 8 is abnormal, the abnormality of the yaw rate sensor 8can be detected with greater accuracy.

FIG. 6 show a fourth embodiment of the present invention, whereinportions or components corresponding to those in each of theabove-described embodiments are designated by like reference characters.

To detect the abnormality of the yaw rate sensor 8 and the lateralacceleration sensor 9, the control unit 5 includes a vehicle speedpresuming means 11, a multiplying means 19, a dividing means 22, alow-select means 25 for selecting lower one of outputs from themultiplying means 19 and the dividing means 22, a yaw rate sensorabnormality determining means 26 for determining the abnormality of theyaw rate sensor 8 based on an output from the low-select means 25 and ayaw rate γ detected by the yaw rate sensor 8, a dividing means 16, alow-select means 17 for selecting lower one of an output from thedividing means 16 and the gravitational acceleration G, and a lateralacceleration sensor abnormality determining means 18 for determining theabnormality of the lateral acceleration sensor 9 based on an output fromthe low-select means 17 and the lateral acceleration α detected by thelateral acceleration sensor 9.

In the yaw rate sensor abnormality determining means 26, a valueoutputted from the low-select means 25, i.e., min{(δ·V·k), (α/V)} andthe yaw rate γ detected by the yaw rate sensor 8 are compared with eachother. If γ>min{(δ·V·k), (α/V)}, the yaw rate sensor abnormalitydetermining means 26 determines that the yaw rate sensor 8 is abnormal,thereby outputting a signal indicative of the fact that the yaw ratesensor 8 is abnormal.

By replacing (V/R) in FIG. 3 by (δ·V·k) as described in the second andthird embodiments, a range of γ capable of actually being produced canbe determined more precisely. Therefore, in the fourth embodiment inwhich when γ>min{(δ·V·k), (α/V)}, it is determined that the yaw ratesensor 8 is abnormal, the accuracy of the detection of the abnormalityof the yaw rate sensor 8 is further enhanced.

FIGS. 7 and 8 show a fifth embodiment of the present invention, whereinportions or components corresponding to those in each of theabove-described embodiments are designated by like reference characters.

To detect the abnormality of the yaw rate sensor 8 and the lateralacceleration sensor 9, the control unit 5 includes a vehicle speedpresuming means 11, a multiplying means 19, a dividing means 22, alow-select means 25 for selecting lower one of outputs from themultiplying means 19 and the dividing means 22, a yaw rate sensorabnormality determining means 26 for determining the abnormality of theyaw rate sensor 8 based on an output from the low-select means 25 and ayaw rate γ detected by the yaw rate sensor 8, a multiplying means 27, alow-select means 28 for selecting a lower one of an output from themultiplying means 27 and the gravitational acceleration G, and a lateralacceleration sensor abnormality determining means 29 for determining theabnormality of the lateral acceleration sensor 9 based on an output fromthe low-select means 28 and the lateral acceleration α detected by thelateral acceleration sensor 9.

The vehicle speed V obtained in the vehicle speed presuming means 11 andthe steering angle δ detected by the steering angle sensor 7 areinputted to the multiplying means 27. In the multiplying means 27, thecalculation of multiplying the steering angle δ by a squared value (V²)of the vehicle speed V and a given constant k is carried out. Thelow-select means 28 selects a lower one of a value (δ·V² ·k) obtained inthe multiplying means 27 and the gravitational acceleration G, andinputs such lower one to the lateral acceleration sensor abnormalitydetermining means 29.

In the lateral acceleration sensor abnormality determining means 29, theabnormality of the lateral acceleration sensor 9 is determined in aprocedure as shown in FIG. 8. At Step S1, it is determined whether thelateral acceleration α is greater than zero. Here, α>0 indicates a statein which the vehicle is being turned rightwards; α<0 indicates a statein which the vehicle is being turned leftwards, and α=0 indicates thestate in which at a state in which the vehicle is traveling straight. Ifit is determined at Step S1 that α>0, i.e., when the vehicle is beingturned rightwards, the process is advanced from Step S1 to Step S2.

At Step S2, it is determined whether the lateral acceleration α isgreater than the output min{(δ·V² ·k), G} from the low-select means 28.If it is determined at Step S2 that α>min{(δ·V² ·k), G}, a rightabnormality flag is set at "1" at Step S3. Namely, it is determined thatlateral acceleration sensor 9 is abnormal, when the vehicle is beingturned rightwards.

At Step S4, it is determined whether a left abnormality flag is at "1".If the left abnormality flag is at "1", it is determined at Step S5 thatthe lateral acceleration sensor 9 is abnormal.

If it is determined at Step S1 that α≦0, i.e., it is determined that thevehicle is being turned leftwards, or is traveling straight, the processis advanced from Step S1 to Step S6, at which it is determined whetherthe lateral acceleration α is less than a value [-min{(δ·V² ·k), G}]obtained by adding a minus sign to the output from the low-select means28. If it is determined that ∝<-min{(δ·V² ·k), G}, the left abnormalityflag is set at "1" at Step S7. Namely, it is determined that the lateralacceleration sensor 9 is abnormal, when the vehicle is being turnedleftwards.

At Step S8, it is determined whether the right abnormality flag is at"1". If the right abnormality flag is at "1", it is determined at StepS5 that the lateral acceleration sensor 9 is abnormal.

In any of the following cases: (1) when it is determined at Step S2 thatα≦min{(δ·V² ·k), G}; (2) when it is determined at Step S4 that the leftabnormality flag is at "0"; (3) when it is determined at Step S6 thatα≧-min{(δ·V² ·k), G}; (4) when it is determined at Step S8 that theright abnormality flag is at "0"; and (5) after it is determined at StepS5 that the lateral acceleration sensor 9 is abnormal, the process isadvanced to Step S9. When it is confirmed at Step S9 that a given timehas elapsed, both of the left and right flags are reset at Step S10.

According to such abnormality determining process shown in FIG. 8, whenthe lateral acceleration α exceeds the output min{(δ·V² ·k), G} from thelow-select means 28 in either of the left and right directions, it isdetermined in the lateral acceleration sensor abnormality determiningmeans 29 that the lateral acceleration sensor 9 is abnormal.

By replacing (V/R) in FIG. 3 by (δ·V·k) as described in the secondembodiment, a range of yaw rate γ capable of being actually produced canbe determined more precisely than the obliquely-lined range shown inFIG. 3. In a range of smaller side-slip, a relation, γ=(α/V) isestablished. Therefore, if the range of yaw rate γ determined accordingto γ≦min{(δ·V·k), (G/V)} is replaced by the lateral acceleration α, arelation, α≦min{(δ·V² ·k), G}, is given. Therefore, in the fifthembodiment in which when the lateral acceleration α is greater thanmin{(δ·V² ·k), G}, it is determined that the lateral acceleration sensor9 is abnormal, the accuracy of the detection of the abnormality of thelateral acceleration sensor 9 is enhanced. Moreover, an offset valuecomponent corresponding to an inclination of a road surface is includedin the value obtained in the lateral acceleration sensor 9. However,only when the lateral acceleration sensor abnormality determining means29 determines that the lateral acceleration sensor 9 is abnormal, bothof when the vehicle is being turned leftwards and rightwards, thelateral acceleration sensor abnormality determining means 29 determinesthat the lateral acceleration sensor 9 is abnormal. Therefore, theerroneous determination due to the sloping of the road surface can beavoided, whereby abnormality of the lateral acceleration sensor 9 can bedetected with greater accuracy.

Although the embodiments of the present invention have been described indetail, it will be understood that the present invention is not limitedto the above-described embodiments, and various modifications may bemade without departing from the subject matter of the present inventiondefined in claims.

What is claimed:
 1. A system for detecting an abnormality of a yaw ratesensor, comprising:a vehicle speed detecting means for detecting avehicle speed of a vehicle; a first dividing means for dividing thevehicle speed detected by said vehicle speed detecting means by aminimum turning radius of the vehicle; a second dividing means fordividing a gravitational acceleration by the vehicle speed detected bysaid vehicle speed detecting means; a low-select means for selecting alower one of outputs from both of said first and second dividing means;and an abnormality determining means for determining that a yaw ratesensor is abnormal when a yaw rate detected by said yaw rate sensorexceeds a value selected by said low-select means.